1. Field of the Invention
The invention relates to a tiltable Z-axis platform, and more particularly, the invention relates to a tiltable Z-axis platform for supporting and moving a robotic arm or other mechanism.
2. Brief Description of the Related Art
In the semiconductor wafer and flat panel display processing fields, robot arms are used in moving substrates including semiconductor wafers and flat panel displays to and from cassettes and workstations where the substrates are stored and various processing steps take place. The robot arm and the workstations or cassettes where the substrates are held must be aligned with one another so that the substrates can be transferred and positioned properly without damage.
Several different types of robot arm linkages are known in the art. These linkages include telescoping arms, rotatable link arms, and isosceles triangle-type linkages. Telescoping arms include multiple members slidable with respect to one another to allow linear extension of the arm.
More commonly used robot arms include two or more links which are pivotally connected to one another to form an arm in which the links are pivoted in a coordinated manner to extend and retract the arm. Pulleys, belts, and motors are generally utilized to move the links of the robot arm with respect to one another and to move a robot end effector or hand located at the end of the arm which is used to grasp and transport a substrate. In use, the robot arm is extended to a location of a substrate positioned in a cassette or at a workstation and picks up the substrate with the end effector generally by vacuum. The arm is then retracted and rotated to the position of another cassette or workstation. The robot arm carrying the substrate is then advanced to the cassette or workstation where the substrate is deposited.
In some situations it would be desirable to be able to tilt a robotic arm mechanism, as a whole about a Z-axis, so as to allow better alignment of the robot for a particular task. One situation in which a tiltable Z-axis robot would be desirable is during the unloading of substrates from a cassette. In typical semiconductor wafer cassettes, a plurality of semiconductor wafers are stacked one above the other and spaced apart from one another. The wafers are supported in the cassette by a narrow ledge at the periphery of the wafers in order to avoid or minimize contamination of the wafers. Occasionally, one of the wafers in the cassette is loaded in a misaligned configuration or slips off of a portion of the ledge during transport. In such a situation, a tiltable Z-axis platform allows the robot to be tilted to accommodate such a misalignment of a substrate.
Another problem occurring during manipulation of substrates, including semiconductor wafers and flat panels, is that the Z-axis of the robotic arm may not be completely parallel to the axis of a cassette or workstation at which the substrate is positioned. The relative tilt between the robot and the cassette or workstation may be only a few degrees. However, this misalignment prevents the robot arm from being able to properly approach and pick up the substrate with the end effector and properly place the substrate in a cassette or workstation.
Adjustment of the Z-axis of a robotic arm is also useful when transporting large substrates which may deflect the robot arm slightly downward due to the substrate weight. An adjustable Z-axis platform may be used to compensate for deflections of the robot arm under the weight of a substrate to align the substrate with a workstation or cassette.
Robot arms having universally tiltable Z-axes to accommodate misalignments are disclosed in U.S. patent applications Ser. No. 08/661,292, filed Jun. 13, 1996; Ser. No. 08/788,898, filed Jan. 23, 1997; and Ser. No. 08/889,907, filed Jul. 10, 1997, each of which is incorporated herein by reference in its entirety. The universally tiltable Z-axis robots described in the previously filed applications include one or more platforms which are tiltable in multiple directions. However, the mechanisms used for these universally tiltable Z-axis platforms are relatively complex and expensive.
Accordingly, it would be desirable to provide a universally tiltable Z-axis platform with a simpler and less costly construction. In addition, in some circumstances it may be desirable to provide a uni-directional tiltable platform for supporting a robotic arm mechanism or other mechanisms.